Human obesity is a recognized health problem with approximately ninety-seven million people considered clinically overweight in the United States. The accumulation or maintenance of body fat bears a direct relationship to caloric intake. Therefore, one of the most common methods for weight control to combat obesity is the use of relatively low-fat diets, that is, diets containing less fat than a xe2x80x9cnormal dietxe2x80x9d or that amount usually consumed by the patient.
The presence of fats in a great many food sources greatly limits the food sources which can be used in a low fat diet. Additionally, fats contribute to the flavor, appearance and physical characteristics of many foodstuffs. As such, the acceptability of low-fat diets and the maintenance of such diets are difficult.
Various chemical approaches have been proposed for controlling obesity. Anorectic agents such as dextroamphetamine, the combination of the non-amphetamine drugs phentermine and fenfluramine (Phen-Fen), and dexfenfluramine (Redux) alone, are associated with serious side effects. Indigestible materials such as olestra (OLEAN(copyright)), mineral oil or neopentyl esters (see U.S. Pat. No. 2,962,419) have been proposed as substitutes for dietary fat. Garcinia acid and derivatives thereof have been described as treating obesity by interfering with fatty acid synthesis. Swellable crosslinked vinyl pyridine resins have been described as appetite suppressants via the mechanism of providing non-nutritive bulk, as in U.S. Pat. No. 2,923,662. Surgical techniques such as temporary ileal bypass surgery, are employed in extreme cases.
However, methods for treating obesity, such as those described above have serious shortcomings with controlled diet remaining the most prevalent technique for controlling obesity. As such, new methods for treating obesity are needed.
The invention features a method for treating obesity in a patient by administering to the patient a polymer that has been substituted with or comprises one or more groups which can inhibit a lipase. Lipases are key enzymes in the digestive system which break down tri- and diglycerides, which are too large to be absorbed by the small intestine into fatty acids which can be absorbed. Therefore, inhibition of lipases results in a reduction in the absorption of fat. In one embodiment, the lipase inhibiting group can be a xe2x80x9csuicide substratexe2x80x9d which inhibits the activity of the lipase by forming a covalent bond with the enzyme either at the active site or elsewhere. In another embodiment, the lipase inhibiting group is an isosteric inhibitor of the enzyme. The invention further relates to the polymers employed in the methods described herein as well as novel intermediates and methods for preparing the polymers.
The invention features a method for treating obesity in a patient by administering to the patient a polymer comprising one or more groups which can inhibit a lipase. Since lipases are responsible for the hydrolysis of fat, a consequence of their inhibition is a reduction in fat hydrolysis and absorption. The invention further relates to the polymers employed in the methods described herein as well as novel intermediates and methods for preparing the polymers.
In one aspect of the invention, the lipase inhibiting group inactivates a lipase such as gastric, pancreatic and lingual lipases. Inactivation can result by forming a covalent bond such that the enzyme is inactive. The covalent bond can be formed with an amino acid residue at or near the active site of the enzyme, or at a residue which is distant from the active site provided that the formation of the covalent bond results in inhibition of the enzyme activity. Lipases contain a catalytic triad which is responsible for the hydrolysis of lipids into fatty acids. The catalytic triad consists of a serine, aspartate and histidine amino acid residues. This triad is also responsible for the hydrolysis of amide bonds in serine proteases, and it is expected that compounds that are serine protease inhibitors will also inhibit lipases. Therefore, serine protease inhibitors that can be covalently linked to a polymer are preferred lipase inhibiting groups. For example, a covalent bond can be formed between the lipase inhibiting group and a hydroxyl at or the catalytic site of the enzyme. For instance, a covalent bond can be formed with serine. Inactivation can also result from a lipase inhibiting group forming a covalent bond with an amino acid, for example cysteine, which is at some distance from the active site. In addition, non-covalent interaction between the lipase inhibiting group and the enzyme can also result in inactivation of the enzyme. For example, the lipase inhibiting group can be an isostere of a fatty acid, which can interact non-covalently with the catalytic site of the lipase. In addition, the lipase inhibiting group can compete for lipase hydrolysis with natural triglycerides.
In one aspect of the invention, a lipase inhibiting group can be represented by formula I: 
wherein,
R is a hydrogen, hydrophobic moiety, xe2x80x94NR2R3, xe2x80x94CO2H, xe2x80x94OCOR2, xe2x80x94NHCOR2, a substituted or unsubstituted aliphatic group or a substituted or unsubstituted aromatic group;
R1 is an activating group;
Y is oxygen, sulfur, xe2x80x94NR2xe2x80x94 or is absent;
Z and Z1 are, independently, an oxygen, alkylene, sulfur, xe2x80x94SO3xe2x80x94, xe2x80x94CO2xe2x80x94, xe2x80x94NR2xe2x80x94, xe2x80x94CONR2xe2x80x94, xe2x80x94PO4Hxe2x80x94 or a spacer group;
R2 and R3 are, independently, a hydrogen, a substituted or unsubstituted aliphatic group, or a substituted or unsubstituted aromatic group;
m is 0 or 1; and
n is 0 or 1.
In one embodiment, the lipase inhibiting group of formula I can be represented by the following structures: 
wherein R, R1 and Y are defined as above.
In another embodiment, the lipase inhibiting group of structural formula I can be represented by the following structures: 
wherein R, R1, R2, R3 and Y are defined as above, and p is an integer (e.g. an integer between zero and about 30, preferably between about 2 and about 10).
In another embodiment, the lipase inhibitor of formula I is a mixed anhydride. Mixed anhydrides include, but are not limited to, phosphoric-carboxylic, phosphoric-sulfonic and pyrophosphate mixed anhydride lipase inhibiting groups which can be represented by the following structures, respectively: 
wherein R, R1, Y and Z1 are defined as above.
In another aspect, a lipase inhibiting group of the invention can be an anhydride. In one embodiment, the anhydride is a cyclic anhydride represented by formula II: 
wherein R, Z and p are defined as above, X is xe2x80x94PO2xe2x80x94, xe2x80x94SO2xe2x80x94 or xe2x80x94COxe2x80x94, and k is an integer from 1 to about 10, preferably from 1-4.
In another embodiment, the anhydride lipase inhibiting groups can be a cyclic anhydride which is part of a fused ring system. Anhydrides of this type can be represented by formula III: 
wherein X and Z are defined as above, and ring A is an optionally substituted cyclic aliphatic group or aromatic group, or combinations thereof, which can include one or more heteroatoms in the ring. In a particular embodiment, the cyclic anhydride is a benzenesulfonic anhydride represented by the following structure: 
wherein Z is defined as above and the benzene ring can be further substituted.
In another aspect, the lipase inhibiting group is an xcex1-halogenated carbonyl which can be represented by formula IV: 
wherein R and Y are defined as above, and W1 and W2 are each independently hydrogen or halogen, for example, xe2x80x94F, xe2x80x94Cl, xe2x80x94Br, and xe2x80x94I, wherein at least one of W1 and W2 is a halogen.
In yet another aspect, a cyclic compound having an endocyclic group that is susceptible to nucleophilic attack can be a lipase inhibiting group. Lactones and epoxides are examples of this type of lipase inhibiting group and can be represented by formulas V and VI, respectively: 
wherein R, Z, m and p are defined as above.
In a further aspect, the lipase inhibiting group can be a sulfonate or disulfide group represented by formulas VII and VIII, respectively: 
wherein R, Z and p are defined as above, and R5 is absent or a hydrophobic moiety, a substituted or unsubstituted aliphatic group or a substituted or unsubstituted aromatic group.
In a particular embodiment, the disulfide lipase inhibiting group can be represent by the following formula: 
wherein R, Z and p are defined as above.
In a further aspect of the invention, a lipase inhibiting group can be a boronic acid which can be linked to a polymer by a hydrophobic group or to the polymer directly when the polymer is hydrophobic. Boronic acid lipase inhibiting groups can be represented by the following structure: 
wherein R5, Z, n and m are defined as above.
In an additional aspect, an isosteric lipase inhibiting group can be a phenolic acid linked to the polymer. Phenolic acid lipase inhibiting groups can be represented by the following structure: 
wherein Z, R5, n and m are defined as above and xe2x80x94CO2H and xe2x80x94OH are ortho or para with respect to each other.
A variety of polymers can be employed in the invention described herein. The polymers can be aliphatic, alicyclic or aromatic or synthetic or naturally occurring. However, aliphatic and alicyclic synthetic polymers are preferred. Furthermore, the polymer can be hydrophobic, hydrophilic or copolymers of hydrophobic and/or hydrophilic monomers. The polymer can be non-ionic (e.g., neutral), anionic or cationic, in whole or in part. Furthermore, the polymers can be manufactured from olefinic or ethylenic monomers (such as vinylalcohol) or condensation polymers.
For example, the polymers can be a polyvinylalcohol, polyvinylamine, poly-N-alkylvinylamine, polyallylamine, poly-N-alkylallylamine, polyalkylenimine, polyethylene, polypropylene, polyether, polyethylene oxide, polyamide, polyacrylic acid, polyalkylacrylate, polyacrylamide, polymethacrylic acid, polyalkylmethacrylate, polymethacrylamide, poly-N-alkylacrylamide, poly-N-alkylmethacrylamide, polystyrene, vinylnaphthalene, ethylvinylbenzene, aminostyrene, vinylbiphenyl, vinylanisole, vinylimidazolyl, vinylpyridinyl, dimethylaminomethylstyrene, trimethylammoniumethylmethacrylate, trimethylammoniumethylacrylate, carbohydrate, protein and substituted derivatives of the above (e.g., fluorinated monomers thereof) and copolymers thereof.
Preferred polymers include polyethers, such as polyalkylene glycols. Polyethers can be represented by the formula IX: 
wherein R is defined as above and q is an integer.
For example, the polymer can be polypropylene glycol or polyethylene glycol or copolymers thereof. The polymers can be random or block copolymers. Also, the polymers can be hydrophobic, hydrophilic, or a combination thereof (as in random or block polymers).
A particularly preferred polymer is a block copolymer characterized by hydrophobic and hydrophilic polymeric regions. In such an embodiment, the xe2x80x9ccore polymer can be hydrophobic with one or both ends capped with a hydrophilic polymer or vice versa. An example of such a polymer is a polyethyleneglycol-polypropyleneglycol-polethyleneglycol copolymer, as is sold under the tradename PLURONIC(copyright) (BASF Wyandotte Corp.). BRIJ(copyright) and IGEPAL(copyright) (Aldrich, Milwaukee, Wis.) are examples of polymers having a polyethylene glycol core capped withe a hydrophobic end group. BRIJ(copyright) polymers are polyethylene glycols having one end capped with alkoxy group, while the hydroxy group at the other end of the polymer chain is free. IGEPAL(copyright) polymers are polyethylene glycols having one end capped with 4-nonylphenoxy group, while the hydroxy group at the other end of the polymer chain is free.
Another class of polymers includes aliphatic polymers such as, polyvinylalcohol, polyallylamine, polyvinylamine and polyethylenimine. These polymers can be further characterized by one or more substituents, such as substituted or unsubstituted, saturated or unsaturated alkyl and substituted or unsubstituted aryl. Suitable substituents include anionic, cationic or neutral groups, such as alkoxy, aryl, aryloxy, aralkyl, halogen, amine, and ammonium groups, for example. The polymer can desirably possess one or more reactive functional groups which can, directly or indirectly, react with an intermediate possessing the lipase inhibiting groups.
In one embodiment, the polymers have the following repeat unit: 
wherein,
q is an integer; and
R4 is xe2x80x94OH, xe2x80x94NH2, xe2x80x94CH2NH2, xe2x80x94SH, or a group represented by the following formula: 
wherein R, R1, Y, Z, Z1, m and n are defined as above.
Additionally, the polymer can be a carbohydrate, such as chitosan, cellulose, hemicellulose or starch or derivatives thereof.
The polymer can be linear or crosslinked. Crosslinking can be performed by reacting the copolymer with one or more crosslinking agents having two or more functional groups, such as electrophilic groups, which react with an alcohol of the polymer to form a covalent bond. Crosslinking in this case can occur, for example, via nucleophilic attack of the polymer hydroxy groups on the electrophilic groups. This results in the formation of a bridging unit which links two or more alcoholic oxygens from different polymer strands. Suitable crosslinking agents of this type include compounds having two or more groups selected from among acyl chloride, epoxide, and alkyl-X, wherein X is a suitable leaving group, such as a halo, tosyl or mesyl group. Examples of such compounds include, but are not limited to, epichlorohydrin, succinyl dichloride, acryloyl chloride, butanedioldiglycidyl ether, ethanedioldiglycidyl ether, pyromellitic dianhydride, and dihaloalkanes.
The polymer composition can also be crosslinked by including a multifunctional co-monomer as the crosslinking agent in the reaction mixture. A multifunctional co-monomer can be incorporated into two or more growing polymer chains, thereby crosslinking the chains. Suitable multifunctional co-monomers include, but are not limited to, diacrylates, triacrylates, and tetraacrylates, dimethacrylates, diacrylamides, diallylacrylamides, and dimethacrylamides. Specific examples include ethylene glycol diacrylate, propylene glycol diacrylate, butylene glycol diacrylate, ethylene glycol dimethacrylate, butylene glycol dimethacrylate, methylene bis(methacrylamide), ethylene bis(acrylamide), ethylene bis(methacrylamide), ethylidene bis(acrylamide), ethylidene bis(methacrylamide), pentaerythritol tetraacrylate, trimethylolpropane triacrylate, bisphenol A dimethacrylate, and bisphenol A diacrylate. Other suitable multifunctional monomers include polyvinylarenes, such as divinylbenzene.
The molecular weight of the polymer is not critical. It is desirable that the polymer be large enough to be substantially or completely non-absorbed in the GI tract. For example, the molecular weight can be more than 900 Daltons.
The digestion and absorption of lipids is a complex process in which water insoluble lipids are emulsified to form an oil in water emulsion with an oil droplet diameter of approximately 0.5 mm. This emulsified oil phase has a net negative charge due to the presence of fatty acids and bile salts, which are the major emulsifying agents. Lipases that are present in the aqueous phase hydrolyze the emulsified lipids at the emulsion surface. Most lipases contain an active site that is buried by a surface loop of amino acids that sit directly on top of the active site when the lipase is in an aqueous solution. However, when the lipase comes in contact with bile salts at the lipid/water interface of a lipid emulsion, the lipase undergoes a conformational change that shifts the surface loop to one side and exposes the active site. This conformational change allows the lipase to catalyze hydrolysis of lipids at the lipid/water interface of the emulsion. Polymers that disrupt the surface of the emulsion or alter its chemical nature are expected to inhibit lipase activity. Therefore, it may increase the effectiveness of polymers that have lipase inhibiting groups to administer them with one or more polymers that alter the emulsion surface. Alternatively, lipase inhibiting groups can be attached directly to such a polymer.
Several types of fat-binding polymers have been effective in disrupting the surface of the lipid emulsion or altering its chemical nature. For example, polymers that have positively charged emulsifiers are able to form stable polycation lipid emulsions. The lipids in such an emulsion are not substrates for gastrointestinal lipases because the surface of the emulsion has a net positive charge instead of the usual net negative charge. Another type of fat-binding polymer destabilizes the emulsion causing the oil droplets of the emulsion to coalesce. This decreases the emulsion surface area where lipases are active, and therefore, reduces lipid hydrolysis. Fat-binding polymer are further defined in copending application Ser. No. 09/004,963, filed on Jan. 9, 1998, and application Ser. No. 09/166,453, filed on Oct. 5, 1998, the contents of which are incorporated herein by reference.
The substituted polymers described herein can be manufactured according to methods generally known in the art. For example, a lipase inhibiting intermediate characterized by a reactive moiety can be contacted with a polymer characterized by a functional group which reacts with said reactive moiety. See March, J., Advanced Organic Chemistry, 3rd edition, John Wiley and Sons, Inc.; New York, (1985).
A xe2x80x9chydrophobic moiety,xe2x80x9d as the term is used herein, is a moiety which, as a separate entity, is more soluble in octanol than water. For example, the octyl group (C8H17) is hydrophobic because its xe2x80x9cparentxe2x80x9d alkane, octane, has greater solubility in octanol than in water. The hydrophobic moieties can be a saturated or unsaturated, substituted or unsubstituted hydrocarbon group. Such groups include substituted and unsubstituted, normal, branched or cyclic aliphatic groups having at least four carbon atoms, substituted or unsubstituted arylalkyl or heteroarylalkyl groups and substituted or unsubstituted aryl or heteroaryl groups. Preferably, the hydrophobic moiety includes an aliphatic group of between about six and thirty carbons. Specific examples of suitable hydrophobic moieties include the following alkyl groups: butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, docosanyl, cholesteryl, farnesyl, aralkyl, phenyl, and naphthyl, and combinations thereof. Other examples of suitable hydrophobic moieties include haloalkyl groups of at least fourcarbons (e.g., 10-halodecyl), hydroxyalkyl groups of at least six carbons (e.g., 11-hydroxyundecyl), and aralkyl groups (e.g., benzyl). As used herein aliphatic groups include straight, chained, branched or cyclic C4-C30 hydrocarbons which are completely saturated or contain one or more units of unsaturation.
Aromatic groups suitable for use in the invention include, but are not limited to, aromatic rings, for example, phenyl and substituted phenyl, heteroaromatic rings, for example, pyridinyl, furanyl and thiophenyl, and fused polycyclic aromatic ring systems in which a carbocyclic aromatic ring or heteroaryl ring is fused to one or more other carbocyclic or heteroaryl rings. Examples of fused polycyclic aromatic ring systems include substituted or unsubstituted phenanthryl, anthracyl, naphthyl, 2-benzothienyl, 3-benzothienyl, 2-benzofuranyl, 3-benzofuranyl, 2-indolyl, 3-indolyl, 2-quinolinyl, 3-quinolinyl, 2-benzothiazole, 2-benzooxazole, 2-benzimidazole, 2-quinolinyl, 3-quinolinyl, 1-isoquinolinyl, 3-quinolinyl, 1-isoindolyl, 3-isoindolyl, and acridintyl.
A xe2x80x9csubstituted aliphatic or aromatic groupxe2x80x9d can have one or more substituents, e.g., an aryl group (including a carbocyclic aryl group or a heteroaryl group), a substituted aryl group, xe2x80x94O-(aliphatic group or aryl group), xe2x80x94O-(substituted aliphatic group or substituted aryl group), acyl, xe2x80x94CHO, xe2x80x94CO-(aliphatic or substituted aliphatic group), xe2x80x94CO-(aryl or substituted aryl), xe2x80x94COO-(aliphatic or substituted aliphatic group), xe2x80x94COO-(aryl or substituted aryl group), xe2x80x94NH-(acyl), xe2x80x94O-(acyl), benzyl, substituted benzyl, halogenated lower alkyl (e.g. trifluoromethyl and trichloromethyl), fluoro, chloro, bromo, iodo, cyano, nitro, xe2x80x94SH, xe2x80x94S-(aliphatic or substituted aliphatic group), xe2x80x94S-(aryl or substituted aryl), xe2x80x94S-(acyl) and the like.
An xe2x80x9cactivating groupxe2x80x9d is a group that renders a functional group or moiety reactive. Generally, electron withdrawing groups are xe2x80x9cactivating groups.xe2x80x9d R1 or Yxe2x80x94R1, of the above formulae, is preferably a good leaving group or an electron withdrawing group. Examples of good leaving groups are phosphate, p-nitrophenol, o,p-dinitrophenol, N-hydroxysuccinimide, imidazole, ascorbic acid, pyridoxine, trimethylacetate, adamantanecarbonylate, p-chlorophenol, o,p-dichlorophenol, methanesulfonylate, mesitylsulfonylate and triisopropylbenzenesulfonylate. A preferred leaving group is N-hydroxysuccinimide.
A spacer group can be a group that has one to about thirty atoms and is covalently bonded to the lipase inhibitor, to the polymer, or to the hydrophobic moiety. Generally, the spacer group can be covalently bonded to the lipase inhibitor, polymer or hydrophobic moiety through a functional group. Examples of functional groups are oxygen, alkylene, sulfur, xe2x80x94SO2xe2x80x94, xe2x80x94CO2xe2x80x94, xe2x80x94NR2xe2x80x94, or xe2x80x94CONR2xe2x80x94. A spacer group can be hydrophilic or hydrophobic. Examples of spacer groups include amino acids, polypeptides, carbohydrates, and optionally substituted alkylene or aromatic groups. Spacer groups can be manufactured from, for example, epichlorohydrin, dihaloalkane, haloalkyl esters, polyethylene glycol, polypropylene glycol and other cross-linking or difunctional compounds. Bromoalkylacetate is a preferred spacer group.
The amount of a polymer administered to a subject will depend on the type and severity of the disease and on the characteristics of the subject, such as general health, age, body weight and tolerance to drugs. It will also depend on the degree of obesity and obesity related complications. The skilled artisan will be able to determine appropriate dosages depending on these and other factors. Typically, in human subjects, an effective amount of the polymer can range from about 10 mg per day to about 50 mg per day for an adult. Preferably, the dosage ranges from about 10 mg per day to about 20 mg per day.
The polymer can be administered by any suitable route, including, for example, orally in capsules, suspensions or tablets. Oral administration by mixing with food is a preferred mode of administration.
The polymer can be administered to the individual in conjunction with an acceptable pharmaceutical carrier as part of a pharmaceutical composition. Formulation of a polymer to be administered will vary according to the route of administration selected (e.g., solution, emulsion, capsule). Suitable pharmaceutical carriers may contain inert ingredients which do not interact with the lipase inhibiting groups of the polymer. Standard pharmaceutical formulation techniques can be employed, such as those described in Remington""s Pharmaceutical Sciences, Mack Publishing Company, Easton, Pa. Methods for encapsulating compositions (such as in a coating of hard gelatin or cyclodextran) are known in the art (Baker, et al., xe2x80x9cControlled Release of Biological Active Agentsxe2x80x9d, John Wiley and Sons, 1986).
Synthesis of Polymers